1. Field of the Invention
This invention relates to apparatus for controlling hydraulically actuated devices, and in particular to apparatus for remotely controlling hydraulically actuated devices, such as throttling valves.
2. Description of the Prior Art
The use of hydraulic actuator systems to mechanically adjust the position of levers, valve stems and the like is commonplace in a wide variety of activities. For example, fluid flow processes, such as refinery processes and other chemical processes, typically require one or more hydraulically actuated throttling valves to regulate the flow rate of fluids through fluid-conducting conduits. These processes typically require frequent or even substantially continuous repositioning of the throttling mechanism of the throttling valve in order to compensate for changes in liquid levels, pressures, fluid compositions and the like. While such repositioning can be done manually, usually the repositioning of the throttling mechanism is performed automatically by the hydraulic actuator system in response to a signal from an automatic controller. Under normal operating conditions automatic controllers can enhance the efficiency of the process unit of which they are a part.
However, during severe upsets of the process units or during normal start-up or shut-down operations, it is possible for automatic controllers to become unstable and fail to properly compensate for changes in the process conditions. In addition, automatic controllers occasionally malfunction even in an otherwise properly operating process unit. Under such circumstances, rather than aid in the control of the process, the automatic controller may actually hinder an operator's attempts to bring the process unit to the desired operating conditions. Accordingly, most automatic controllers can be inactivated and the throttling mechanism can be manually repositioned by an operator stationed at the throttling valve.
While these prior art methods for overriding a malfunctioning automatic controller may be suitable where there is sufficient manpower to attend the valve and the valve is readily accessible, as a practical matter, such override systems are not suitable in the more complex, highly automated process units of modern refineries and chemical plants. Besides having fewer operators to attend to the throttling valves, such process units generally have more throttling valves, at least several of which are not readily accessible from the central control room. Moreover, the same unit upsets which would require an operator to manually override a valve also require that more operator attention be given to other parts of the process unit in order to find and correct the cause of the upset. For these reasons even a relatively minor problem, such as a plugged hydraulic line between the automatic controller and the throttling valve, could force a complete shutdown of the process unit. For example, a large fluid catalytic cracking (FCC) unit may be shut down at a cost of $50,000 per day by the loss of control of a slide valve due to a malfunctioning automatic controller. Thus a need exists for an apparatus for remotely overriding malfunctioning automatic controllers so as to allow remote manual positioning of the hydraulically-actuated device.
Accordingly, a primary object of this invention is to provide an apparatus for remotely controlling hydraulically-actuated devices.
Another object of the invention is to provide an apparatus for remote manual override of a malfunctioning automatic control valve.
Yet another object of this invention is to provide a simple and effective remote control apparatus for positioning the throttling mechanism of a hydraulically-actuated throttling valve.
Still another object of this invention is to provide a readily installable remote control apparatus which is compatible with the existing control mechanisms of conventional hydraulically-actuated throttling valves.
Other objects, advantages and features of this invention will become apparent to those skilled in the art from the following description when taken in conjunction with the accompanying drawing.